题目下列各式由左到右边的变形中,是分解因式的是（ ）A.m(x+y)=mx+mym\left(x+y\right)=mx+mym(x+y)=mx+myB.x2−2x+1=x(x−2)+1x^{2}-2x+1=x\left(x-2\right)+1x2−2x+1=x(x−2)+1C.a2+1=a(a+1a){a}^{2}+1=a(a+\frac{1}{a})a2+1=a(a+a1)D.9x2−3x=3x(3x−1)9x^{2}-3x=3x\left(3x-1\right)9x2−3x=3x(3x−1)知识点：十字相乘法章节：数与式 / 因式分解
